In the manufacture of integrated circuits, photolithography process is an important stage. The line width of integrated circuits is smaller than half micron meter according to the technology development in recent years. The fine patterns of integrated circuits are formed by transferring patterns on reticles onto semiconductor substrates in photolithography processes. However, the patterns, which can be formed by using a specified photolithography process, have linewidths not less than a critical dimension of the process. Besides, the critical dimension of a photolithography process generated by conventional lithography equipment is hard to change.
The integrated circuits with small critical dimensions has higher integrity and operation speed than that with larger critical dimension. Thus, it becomes a trend to diminish the critical dimension of integrated circuits. As a pattern is formed on a substrate by using photolithography technology, the critical dimension of the pattern is not smaller than the critical dimension, which the photolithography process can defined. The limitation of the critical dimension is about 0.13 .mu.m (line=space=0.13 .mu.m) for the present lithography of 248 nm DUV stepper or scanner. The present 248 nm DUV stepper or scanner can not easily solve the line and space less than 0.13 .mu.m, especially for the mass production. The small critical dimension such less than 0.1 .mu.m is unlikely to perform.
In the conventional technology for fabricating integrated circuits, several approaches tried to solve the above problem. For example, phase shift mask (PSM) adapted in photolithography processes has high resolution to define fine patterns on substrates. Another approach is to use short-wavelength light, such as X-ray light, to project small images on substrates. Nevertheless, these approaches could be performed with special lithography equipments.
Therefore, what is needed is a method for fabricating integrated circuits, which has a linewidth less than a critical dimension of photolithography technology.